The present invention relates generally to amplifier circuitry powered by power converter circuits, such as charge pumps and DC-DC converters, and more particularly to improvements which improve the power consumption efficiency of the amplifiers and associated power converter circuits in accordance with the amount of input-signal-dependent load power required from the amplifier and/or power converter circuit.
When a DC-DC converter, such as a charge pump or switching regulator, is used to provide power to an amplifier, the conventional approach is to use a fixed switching frequency and an output voltage amplitude that are determined by the peak power requirement of the worst case load condition. However, in most cases the power requirements of the amplifier load vary greatly over time. For example, the volume settings and dynamic range of music signals output by an audio amplifier to speakers or headphones may have large variations over time. This makes the power converter less power-efficient because it dissipates more power than necessary for a significant portion of the amplifier operating time. If the power converter switching frequency and the amplitude of its output voltage are not chosen for the worst case load condition, then the power converter circuitry may not be able to provide the power required by the amplifier during the signal-dependent peak load demand condition. This results in an undesirable signal-dependent voltage “droop” in the amplifier supply voltage provided by the power converter. This may degrade the performance of the amplifier that drives the load, for example by causing distortion in the output of an audio amplifier powered by the power converter.
The prior art includes a “class G” amplifier which uses feedback from the amplifier's output signal. This allows the amplifier's supply voltage to be reduced when the amplifier's output signal voltage is low and thereby reduces the average power consumption for the amplifier. For example, if at a particular time the amplifier output signal amplitude is small, the amplifier's supply voltage can be reduced without introducing distortion in the amplified output signal. However, this class G feedback approach suffers from a feedback lag whereby the supply voltages provided to the amplifier do not respond/settle fast enough to minimize distortion in the amplification, resulting in undesirable distortion of the output signal produced by the amplifier. Specifically, since the amplifier's supply voltage also must have been adjusted and must have settled prior to the arrival of the amplifier's input signal, delay that occurs during any such feedback technique to adjust the amplifier supply voltage can produce undesirable effects, especially such as causing distortion in the amplifier's output signal. For example, if the amplitude of the amplifier input signal jumps from a low level to a high level, the amplifier's supply voltage may also have to increase to accommodate the power requirements of the load. If the amplifier's supply voltage does not increase fast enough either because of delay through feedback or through a feed-forward loop and/or a DC-DC converter, then, for a short time interval, the amplifier will not have the required voltage “head room” to drive the load without causing distortion of the output signal.
It is believed that there also may be various prior art techniques of feeding forward an incoming analog input signal of an amplifier and controlling the power consumption in the amplifier on the basis of the feed-forward information. However, in these prior art techniques there is always a delay of the feed-forward information. As mentioned above, this also results in undesirable distortion of the output signal produced by the amplifier.
Thus, there is an unmet need for power converter circuitry which is capable of supplying an input-signal-dependent supply voltage to an amplifier to enable it to supply the peak voltages required by a fixed load, wherein the amplifier is energy-efficient during time intervals in which less than peak voltage is required by the load.
There also is an unmet need for power converter circuitry which is capable of supplying an input-signal-dependent supply voltage to an amplifier to enable it to supply the peak current required by a fixed time-independent load, wherein the amplifier is energy-efficient during time intervals in which less than peak current is required by the load.
There also is an unmet need for charge pump circuitry or DC-DC converter circuitry which is capable of supplying power to an amplifier to enable it to supply the peak current required by a fixed load, wherein the power converter circuitry is energy-efficient during time intervals in which less than peak current is required by the load.
There also is an unmet need for a way to avoid distortion in the output of an amplifier powered by a power converter circuit due to signal-dependent ripple and droop in the supply voltage of the amplifier.